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Replacement of Hazardous Chemicals Used in Engineering Plastics with Safe and Renewable Hydrogen-Bond Donor and Acceptor Solvent-Pair Mixtures

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journal contribution
posted on 03.08.2015, 00:00 by Alif Duereh, Yoshiyuki Sato, Richard Lee Smith, Hiroshi Inomata
Mixtures of safe and renewable solvents can replace hazardous solvents presently being used in the manufacture of engineering plastics. In this work, a methodology is proposed for identifying solvent-pair mixtures for preparing polymer precursors, with poly­(amic acid) (PAA) being studied as an example. The methodology uses a chemical safety index, Hansen solubility parameters and Kamlet–Taft solvatochromic parameters of the pure and solvent-pair mixtures to identify hydrogen bond acceptor (HBA)–hydrogen bond donor (HBD) solvent-pair combinations. Ten replacement solvent-pairs for PAA syntheses identified were cyclohexanone–methanol, cyclohexanone–ethanol, cyclopentanone–methanol, cyclopentanone–ethanol, γ-butyrolactone–methanol, γ-butyrolactone–ethanol, γ-butyrolactone–water, γ-valerolactone–methanol, γ-valerolactone–ethanol, and γ-valerolactone–water. Homogeneous PAA solutions could be obtained from HBA–HBD solvent-pair mixtures when their solubility parameters were within 21–29 MPa0.5 and their Kamlet–Taft solvatochromic parameters were π* (>0.67) and β (>0.67) for nonaqueous solutions and π* (>0.68) and β (>0.59) for aqueous solutions. Replacement solvent-pairs, γ-valerolactone–ethanol, γ-valerolactone–water, and γ-butyrolactone–water gave homogeneous precursor solutions that were comparable with commercial solutions prepared with N-methyl-2-pyrrolidone. The proposed methodology and reported solvatochromic parameters make it is possible to identify other solvent-pair mixtures and new solvent-pairs for preparing polymer precursor solutions used in engineering plastics.